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alexfu

mcp-ynab

by alexfu

createTransaction

Add new YNAB transactions individually or in bulk by providing a transaction object or transactions array. Future-dated scheduled transactions are not supported.

Instructions

Creates a single transaction or multiple transactions. If you provide a body containing a transaction object, a single transaction will be created and if you provide a body containing a transactions array, multiple transactions will be created. Scheduled transactions (transactions with a future date) cannot be created on this endpoint.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
plan_idYesThe id of the plan. "last-used" can be used to specify the last used plan and "default" can be used if default plan selection is enabled (see: https://api.ynab.com/#oauth-default-plan).
transactionNo
transactionsNo

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
dataYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A3.9/5.0
Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries the full burden of behavioral disclosure. It correctly signals a mutating create operation and discloses the future-date restriction. However, it does not address auth requirements, failure semantics, or split-transaction limitations, leaving some behavioral context to the input schema.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is front-loaded with the core action, then explains the two input shapes and the exclusion. It is concise and every sentence adds value, though it could be slightly tighter by omitting the repetitive phrase 'will be created.'

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the very rich input schema and existing output schema, the description covers the key selection and invocation facts: single vs. multiple and the scheduled-transaction exclusion. It does not discuss authentication or rate limits, but those are less critical for an agent that already has a plan_id and can rely on the detailed schema.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 33%, so the description should compensate for undocumented top-level parameters. It adds meaning by explaining the transaction/transactions body-shape distinction and the scheduled-date restriction, but it adds little about plan_id or the inner field semantics, which remain schema-dependent.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description uses the specific verb 'Creates' with the resource 'transaction', and clearly distinguishes between single ('transaction' object) and multiple ('transactions' array) creation. It also explicitly excludes scheduled transactions, which distinguishes this tool from the sibling createScheduledTransaction.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives clear context on when to use this tool: for one or many non-scheduled transactions, selected by body shape. It explicitly states that scheduled transactions cannot be created on this endpoint, which is a clear when-not. However, it does not name the alternative tool (createScheduledTransaction) or mention when importTransactions might be preferable.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.